Biological Rhythms

Question 1

sleep and arousal systems are regulated by

Answer 1

biological rhythms, mediated by interaction between SCN & Pineal Gland

Question 2

Suprachiasmatic Nucleus (SCN)

est?

releases?

Answer 2

of Hypothalamus (just anterior to Optic Chiasm) = Circadian Clock

• Establishes free-running rhythm in humans (and other land animals) of activity/rest of ~ 24 +/-1 hours
• Very robust: even if blinded, food-, water-, oxygen-deprived, anesthetized, brain damaged; or isolated cells in tissue culture!
• Genetic: Replace SCN in adult hamster with fetal SCN cells from 20-hour-cycle strain, hamster will adopt 20 hour cycle
• Releases hormones into bloodstream & projects to other Hypothalamic Nuclei, Brainstem, Pituitary glands
• Cycle regulated through projections to and from Pineal Gland (see below)

Question 3

SCN very robust

Answer 3

even if blinded, food-, water-, oxygen-deprived, anesthetized, brain damaged; or isolated cells in tissue culture!

Question 4

SCN genetic

Answer 4

Replace SCN in adult hamster with fetal SCN cells from 20-hour-cycle strain, hamster will adopt 20 hour cycle

Question 5

SCN Releases

Answer 5

hormones into bloodstream & projects to other Hypothalamic Nuclei, Brainstem, Pituitary glands

Question 6

SCN regulated through

Answer 6

projections to and from Pineal Gland (see below)

Question 7

SCN establishes

Answer 7

free-running rhythm in humans (and other land animals) of activity/rest of ~ 24 +/-1 hours

Question 8

Pineal Gland

Answer 8

(just superior to midbrain, posterior to Thalamus)

• Shows daily cycle of production of hormone Melatonin which increases sleepiness
• SCN has receptor sites for Melatonin, so when Pineal increases Melatonin output at end of day, helps regulate cycle
• Melatonin can be taken as sleep aid a few hours before bed, helps reset clock (e.g. anti-Jet Lag)
• Seasonal Affective Disorder (SAD)
• First light of day to SCN via Retino-Hypothalmic Path produces inhibitory output to Pineal

Question 9

Melatonin

Answer 9

can be taken as sleep aid a few hours before bed, helps reset clock (e.g. anti-Jet Lag)

Question 10

Seasonal Affective Disorder (SAD)

Answer 10

= less light in winter, some people over-produce Melatonin;

Light therapy can help

people who live in extremes (no sun in winter)

Question 11

First light of day to SCN via Retino-Hypothalmic Path produces

Answer 11

produces inhibitory output to Pineal

• Decreases Melatonin production, allows wakefulness

Question 12

Together, above interaction becomes your Zeitgeber =

Answer 12

“Time Giver”

• Possible to reset clock, via exposure to bright light, strenuous exercise, seasonal or travel-based changes etc.
• e.g. Receptors in Retina (not Rods or Cones but specialized Ganglions!) w/photopigment Melanopsin react to light
  • These Receptor’s axons synapse in SCN (not in retina or thalamus!) via collateral of Optic Nerve
    = Retino-Hypothalamic-Path

Question 13

Retino-Hypothalamic-Path

Answer 13

Receptor’s axons synapse in SCN (not in retina or thalamus!) via collateral of Optic Nerve

Question 14

Circadian Clock

Answer 14

12 hour dark, 12 hour light

continuous light or dark: active for a certain portion and then it will sleep, the amount of time spent resting and awake is the same but there is a drift (in the absence of any input from the outside world) in time
- flexibility

est. on/off cycle and linking that with the rest of the world

Question 15

SCN

Answer 15

part of the brain that shows 24 hour activity cycle in the cells themselves

ciasm is the place where the two optic nerves cross

direct communication with Pineal Gland

Question 16

Pineal Gland releases

Answer 16

melatonin (sleep aid)

driven by visual circuit called the Retino-Hypothalamic Path

Question 17

Retino-Hypothalamic Path

Answer 17

originates in specialized receptor sites in the eye (ganglion cells)